Do You Need Two A/C Units for a Two-Story Home?

by Gus Stephens

Two A/C units aren't always necessary for a two-story home.

A single A/C unit in a two-story home often produces no-win situations. Crank the thermostat down to offset the natural warming in upstairs living spaces and it’s too chilly downstairs. Make the downstairs comfortable and it’s too hot in the upstairs bedrooms. Installing two separate A/C units dedicated to each level is one answer. It’s also an expensive installation and consumes more energy, boosting operating costs. Two alternatives exist to dual systems that may enable you to live with one central air conditioner.

Reduce Upstairs Heat Gain

A lower cooling load in upstairs living spaces allows more moderate A/C thermostat settings and avoids over-cooling downstairs rooms. During the summer, heat energy accumulating in the attic can raise temperatures up to 150 degrees Fahrenheit. This acute heat conducts through the ceiling into upstairs rooms, offsetting the effect of air conditioning and requiring lower thermostat settings than the rest of the house. Attic fans that exhaust heat and upgraded insulation in the attic floor can reduce attic heat accumulation and keep upstairs rooms cooler without lowering the thermostat.

Install A Zoning System

Zoning divides a single HVAC system into separate cooling zones controlled by independent thermostats. Motorized dampers in the ductwork respond to signals from a central controller to direct cool air to one zone in response to a dedicated thermostat, while simultaneously shutting down or decreasing airflow to another zone that doesn’t require as much cooling. Zone dampers open and close independently of one another. This enables a single air conditioner to maintain different temperatures in upstairs and downstairs zones.

About the Author

Gus Stephens has written about aviation, automotive and home technology for 15 years. His articles have appeared in major print outlets such as "Popular Mechanics" and "Invention & Technology." Along the way, Gus earned a Bachelor of Arts in communications. If it flies, drives or just sits on your desk and blinks, he's probably fixed it.

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